It is very startling when it goes from sincere gratitude to nothing and Istredd's thrown, although he assumes at first that it's because Lucifer is trying to stop sharing feelings. He does have a moment when he thinks Lucifer simply didn't want to engage anymore and poofed off, but luckily he returns and hands a book over.

He takes the book curiously and opens it. That's the Mark you talked about. The one Dean Winchester has. That conversation was an intense one for them, when Istredd said he would protect him, and Istredd decided not to mess with his enemy to keep him out of the middle. He mentioned the 'Father of Murder' and corruption, and what Dean was capable of.

His thumb gently caresses Lucifer's name on the page, seeing it on the list for what it is. It was on your arm, wasn't it? Istredd's noticed him touch it subconsciously. Not that this is of great importance to me but ... will he have to give it to someone else? Will it just keep moving through other people?

Istredd has some invested interest in Free Cities. Geralt and Ciri in particular.